Preparation of plural layer synthetic leather and the like

ABSTRACT

A process for producing a plural-layer synthetic leather whereby (1) a fibrous material is impregnated with a polyurethane containing polymer solution, treated with a nonsolvent for the polymer which nonsolvent is miscible with the solvent of the polymer solution which acts to coagulate the polymer so as to form a porous structure, (2) treating the treated base with an aqueous solution of a solvent or a surfactant and (3) coating the polymer solution onto the pretreated fibrous base and coagulating the polymer with a nonsolvent so as to form a porous structure.

O Umted States Patent 1 1 3,619,257

7 Inventors K8199 Fukada 501 Field 61 Search 117/1355, Y B"; 76 T, 62, 63, 161 KP, 140 R, 47 R, 47 A; 250/30.8, l-liroshi Okamoto, Osaka; Hiroaki Tanaka, 3 2.6 N, 32.8 Osaka, all of Japan 21] App]. No. 748,597 [56] References Cited Filed y 1968 UNITED STATES PATENTS 451 Patented Dim-911971 2 657 151 10/1953 Gensel et a1 117/47 73] Asslgnee gzpmgg 3,067,483 12/1962 HOiiOWe'ii 117/140 x S 3,32 ,5 8 1 1 7 3 .5 32 Priority Aug. 8, 1967 2 6 5/ 967 Gmdne' I H 5 3 3 Japan Primary ExaminerWilliam D. Martin 31 42 5 Assistant Examiner-Theodore G. Davis Attorney-Sughrue, Rothwell, Mion, Zinn & Macpeak ABSTRACT: A process for producing a plural-layer synthetic leather whereby (1) a fibrous material is impregnated with a polyurethane containing polymer solution, treated with a non- PREPARATION OF PLURAL LAYER SYNTHETIC solvent for the polymer which nonsolvent is miscible with the LEATHER AND THE LIKE solvent of the ol mer solution which acts to coa ulate the 15 Claims No Drawings p y g polymer so as to form a porous structure, (2) treating the 52] [1.8. CI 117/76 T, treated base with an aqueous solution ofa solvent or a surfac- 117/62, 117/63, 117/1355, 117/140 A, 1 17 /161 KP tant and (3) coating the polymer solution onto the pretreated 51] Int. Cl 844d l/14, fibrous base and coagulating the polymer with a nonsolvent so as to form a porous structure.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an improved method for the production of plural-layer synthetic leather by forming a porous layer of coagulatedpolymer on a surfaceof a sheet which is made up of a structure in which polymer is coagulated in the porous state between fibers'in a fibrous material. 2. Description of the Prior Art Many investigations concerning synthetic leather have been conducted heretofor and there are now many methods'for producing this type of material. Recently, a synthetic leather preparation by a wet method has gained'considerable attention because it permits the formation of a porous structure with a common film-forming polymer solution which is treated with a miscible nonsolvent for the polymer. Wet'techniques generally result in a porous structure consisting'of a'fibrous base layer and a porous layer of a coagulated polymer. This type of structure not only bears a high resemblance tothe macrostructure of natural leather, but has the good'strength and physical properties normally associated with synthetic leather as well.

That is, in at least one conventional method'for producing synthetic leather by a wet technique, a fibrous material, such as cloth or nonwoven fabric, is impregnated withapolymer solution. The impregnated material is then dipped'into a liquid nonsolvent for the polymer, which is miscible with the polymer solution and which thereby extracts the' solvent and forms a fibrous base. The fibrous base is dipped into thenonsolvent a second time to cause polymer layer to coagulate into a porous structure. Since, in this prior art technique, the polymer solution is coated directly onto the fibrous base without any special pretreatment of the base and'is coagulated in the nonsolvent, the adhesive'property between the base and the coagulated porous polymer layer is not entirely satisfactory. After long periods of use, particularly when subjected to frequent bending stresses, the leatherlike structure has been observed to separate at the interlayer boundaries between the polymer and the fibrous base. Another disadvantage of the prior art techniques is that it is difficult to form a uniform porous structure since the nonsolvent is only capable of coagulating the polymer at the coated layer. According to the present invention, these difficulties of the prior methods may be avoided and a soft synthetic leather comprising a porous polymer layer ofa uniform foam structure, having high interlayer adhesive strength and excellent air and moisture permeability may be obtained.

An object of the invention is therefore to provide a method for the production of synthetic leather having a high interlayer adhesive strength. A further object of the invention is to provide a soft synthetic leather having an excellent air and moisture permeability by forming a porous polymer layer having a more uniform porous structure. Still other objects of the invention will become apparent by the following description.

SUMMARY OF THE INVENTION According to this invention, a plural layer structure can be prepared by a special pretreatment of the fibrous base. The polymer is coagulated in the porous state, and a porous polymer of polyurethane elastomer is coagulated onto the pretreated fibrous base.

That is, the invention relates to a process for the production of plural-layer synthetic leather which comprises (1) impregnating a fibrous material with a polymer solution containing a polyurethane elastomer, treating the impregnated fiber with a liquid which is miscible with the solvent of the polymer solution and which is a nonsolvent for the polymer, which acts to coagulate the polymer into the porous structure thereby obtaining a fibrous base; (2) applying an aqueous solution containing at least one member selected from the groupconsisting of water, one or more solvents for the polyurethane elastomer and surface active agents to said fibrous base; and (3) coating a polyurethane elastomer containing polymer solution onto.

the pretreated fibrous base. Thepolymer is thereafter coagulated into the porous structure by treating-it with a nonsolvent.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In this invention, polymers containing-as a main component, a polyurethane elastomer is preferably used only not only because of its chemical similarity to collagen fibers, which constitutes natural leather, but also because of its resemblance in the coagulated state to natural leather.

The polyurethane elastomermay be obtained by reacting a terminal hydroxy group-containinglinear polymer with an organic diisocyanate and, when desired, a chain extender through the terminal isocyanate group-containing prepolymer. Alternatively, the elastomer may be prepared without going through the prepolymer stage in a solvent or in bulk without a solvent.

The terminal hydroxy group-containing linear polymers are, for example, p'olyesterglycols obtained by reacting dicarboxylic acid compounds with anexcess amount of glycols, polyalkyleneetherglycols obtained by the open ring polymerization of cyclic ethers and polyacetalglycols obtained by the polymerization of aldehyde compounds. Typical: of the organic diisocyanates which may be reacted with the polymers, are for example, toluylene-2,4-diisocyanate, toluylene-2,6- diisocyanate, m-phenylene-diisocyante, biphenylene-4,4- diisocyanate, methylene-bis(4-phenylisocyanate), 4-chloro l,3-phenylenediisocyanate, naphthalenel ,5-diisocyanate, tetramethylene-1,4-diisocyanate, decamethylenel IO-diisocyanate, cyclohexylene-1,4-diisocyanate, tetrahydronaphthalene-diisocyanate and the like.

Chain extenders, such as water, ethylene glycol, diethyl glycol, propylene glycol, hydrazine, ethylene diamine, propylene diamine, tetramethylene diamine, xylylene diamine and the like may be used. When desired, other polymers for example polyamides, polyvinyl acetate, polyvinyl chloride, cellulose acetate, polyacrylonitrile, acrylonitrile-vinyl chloride copolymer, acrylonitrile-butadiene-styrene trepolymer and the like soluble polymers, may be added to the polyurethane elastomers.

When other polymers are added, it is preferable that the polyurethane elastomer be present in an amount of at least 50 percent by weight based on the total weight of the polymers to maintain the superior permeable sheet characteristics of this invention.

One or more of these polymers are dissolved in a solvent, such as acetone, tetrahydrofurane, acetonitril, dimethyl sulfoxide, N,N-dimethyl formamide, N,N-dimethyl acetoamide, tetramethyl urea or a mixture thereof, which is used to impregnate the fibrous material.

The fibrous materials which may be used in the invention are all types of cloth, knitted fabrics and nonwoven fabrics. Suitable fibrous materials are raised or piled cloth, knitted fabrics and fiber mats.

In the impregnation process for the fibrous material with the polymer solution, if the viscosity of the polymer solution is comparatively low, the impregnation may be performed merely by dipping the fibrous material into a bath of the polymer solution. If the viscosity of the solution is greater than 10 cps., forced impregnation, such as by a roller may be adopted to impregnate the interior part.

The fibrous material impregnated with the polymer solution is, then, treated with a nonsolvent for the polymer which is miscible with the solvent of the polymer solution, such as, water, lower alcohols, e.g. methanol and ethanol, ethylene glycol and glycerine, which coagulates the polymer into the porous state. Any convenient method can be used for treating the treated fibrous base with the nonsolvent. For example, the material can be dipped into the nonsolvent bath or the nonsolvent may be applied in a mist by a sprayer or shower or it may be applied in a vapor state.

Thus, to the fibrous base obtained by the above first step, water or an aqueous solution containing at least one member selected from the group consisting of solvents for the polyurethane elastomer and surface active agents is applied.

The water or aqueous solution may be applied to the surface of the fibrous base by a sprayer or shower or the fibrous base may be exposed to an atmosphere of water vapor or may be exposed to an aqueous solution. The most effective method is to dip the fibrous base into water or into an aqueous solution, and thereafter squeezed dry. The amount of the water or aqueous solution applied to the fibrous base is suitably from 20 to 100 percent by weight based on the weight of the fibrous base. If it is less than 20 percent by weight, the desirable effects are not sufficiently achieved and if it is above 100 percent by weight, the polymer solution coated in the third step is rapidly coagulated into the interface between the solution and the fibrous base so that the objects of the invention cannot be achieved.

When using an aqueous solution containing a solvent for the urethane elastomer, such as tetrahydrofurane, acetonitrile N,N-dimethyl formamide, N,N-diethyl formamide and N,N- dimethyl acetoamide, the concentration of the solvent should be less than 90 percent. If an aqueous solvent solution having a high concentration of above 90 percent is used, the polymer film coagulated onto the fibrous base is often redissolved and the coagulating speed of the polymer solution coated on the fibrous base in the third step is decreased, so that the objects of the invention are not sufiiciently achieved.

The surface active agents used in the water or in the aque ous solution of a solvent for the urethane elastomer are, for example, anion surface active agents, such as fatty acid salts and amine salts, cation surface active agents, such as amine salts, nonion surface active agents, such as polyoxyalkylenes and amphoteric surface active agents. The using amount of the surface active agent is less than 1 percent by weight based on the weight ofthe aqueous solution.

According to this invention, the adhesive strength between the fibrous base and the coagulated porous polymer layer is very good. While it is not altogether clear, it is believed that the reason for this good adhesive characteristic is that the contact angle of the polymer solution coated during the third step of the process is decreased by the presence of the water or aqueous solution applied during the second step, improves the so-called wetness. Another possible explanation is that the coagulation of the coated polymer solution proceeds more slowly in the interface.

However, the reason why the objects of the invention are achieved through the second step is unknown since the mechanism behind the coagulating phenomena of the polymer solution is not clear.

in any event, according to this invention, the adhesive strength between each of the interlayers is remarkably good and the polymer layer formed in the third step is coagulated in a uniform foamed structure.

After the second step, a polymer solution containing a polyurethane elastomer as a main component is coated onto the fibrous base and treated with a nonsolvent to coagulate the polymer so as to form a porous structure. The polymer solution used in this step may be the same as that used in the first step. However, according to the desired characteristics for the product, a slightly different composition from that used in the first step may also be used. The coating of the polymer solution may be carried out by extrusion, reverse roll, calender roll or doctor knife methods. When the viscosity of the polymer solution is low, a common coating method, such as spray method, may be adopted.

The nonsolvent treatment for the coagulation of the coated polymer solution layer may be carried out in the same manner as in the first step. The foam structure of the coagulated polymer layer has an important effect upon the touch, feel and physical properties of the product. Generally, when coagulating the polymer solution in the nonsolvent, the foam structure will be affected by the coagulation condition, such as the particular polymer and solvent, the concentration of the solution, the composition of the coagulation bath and the temperature of the coagulation bath. For instance, the foam structure is affected by whether a homogeneous solution is used, or a surface active agent is added, or a heterogeneous polymer solution in small amounts is added, or whether the solution contains an insoluble polymer particle, short fibers, leather powders or inorganic particles, such as magnesium carbonate. By suitably selecting these factors, a synthetic leather having a highly suitable structure can be obtained.

The invention can be more fully illustrated by reference to the following example.

EXAMPLE Five kg. (5 moles) of polypropyleneglycol having a molecular weight of 1,000 was heated at 50 C., and 2.5 kg. (10 moles) of melted diphenylmethane-4,4'-diisocyanate was added. The reaction was carried out at C. for 1.5 hours under the dry air while agitating. The terminal isocyanate group-containing prepolymer containing 5.30 percent of free isocyanate groups was obtained. After cooling the product to 30 C., 11.2 kg. of N,N-dimethyl formamide (DMF) was added and uniformly dissolved. The solution was cooled to 22 C.

To this solution was added a solution obtained by dissolving 250 g. (4.2 moles) of ethylene diamine and 39 g. (0.3 moles) of di-n-butyl amine in 3.0 kg. of DMF over a 10 minute period, while agitating and cooling. Further, 8.0 kg. of DMF was added, so that a solution containing 25 percent of polypropylene-ether-urethaneurea elastomer, having a viscosity of 1 1,000 cps. (at 30 C.) was obtained.

A fibrous material obtained by needling a pile comprising a one-sided raised cotton flannel of 180 g./m.2 and a web of of 200 g./m.2 made of nylon staple of 3 denier X 51 mm. by a needle loom from web side was provided.

The fibrous material was impregnated with said 12 percent polyurethane elastomer solution in DMF, then dipped into water at 45 C. for 3 hours, washed with water and dried. Thus, the fibrous base was obtained.

The predried fibrous base was treated with water or an aqueous solution of DMF or a surface active agent Emulgen 220 (a nonion surface agent produced by Kao Soap KK) in an amount as shown in the following table. A polymer solution prepared as follows was coated on the pretreated fibrous base.

To the above 25 percent polypropylene-ether-urethaneurea elastomer solution in DMF, polyvinyl chloride was added in an amount of 10 parts by weight to parts of the polyurethane elastomer. To the mixed solution, calcium carbonate powder was added in an amount of 25 parts by weight to 100 parts of the polyurethane elastomer, then dispersed uniformly by a homomixer. The defoaming of the mixed solution was carried out under reduced pressure. The solution was coated on above pretreated fibrous base in a thickness of 1.5 mm. with a doctor knife. The coated product was dipped into water at 35 C. for 5 minutes, then transferred into warm water at 65 C. and allowed to stand for 10 minutes.

It was then pressed 10 times between rollers under a linear pressure of4 kg./cm. and dried at l00l05 C. A plural layer synthetic leather was thus obtained which uniform coagulated porous polymer layer was laminated onto the fibrous base and was characterized by a flexible feel.

Themoisture permeability of the leather was 1460 (g./24 hr. m?) and the Garley stiffness was 2910 (mg).

The relation between the applying amount of water or an aqueous solution of DMF or Emulgen 220 to the fibrous base and the adhesive strength was as shown in the following table.

Applied Water or Aqueous Solution Amount Separation Strength 0.2 kgJcm.

Notes:

The applied amount is shown by weight percent to the dry fibrous base.

The destruction of the structure takes place when the adhesive strength of the sample is higher than the separation strength between the fibrous base and the porous polymer layer coagulated thereon, so that it means the destruction of interior layer of the sample.

Thus, a plural-layer synthetic leather having a high adhesive strength between each layer, good flexibility and good moisture permeability, was obtained.

What is claimed is:

l. A process for the production of a plural layer synthetic leather which comprises (1) impregnating a fibrous material as used in the synthetic leather production art with a polymer solution containing a polyurethane elastomer as a major constituent and applying to the impregnated fibrous material a nonsolvent for the polymer which is miscible with the solvent of the polymer solution so as to coagulate the polymer in the porous structure thereby obtaining a fibrous base; (2) applying water or an aqueous solution containing at least one member selected from the group consisting of solvents for the polyurethane elastomer and surface active agents to the fibrous base, said members of the solution interacting wit the already deposited polyurethane elastomer; and (3) coating a polymer solution containing a polyurethane elastomer as a major constituent onto the pretreated fibrous base, and coagulating the polymer in the porous structure by treating it with the nonsolvent. v

2. The process of claim 1 wherein the polymer solution comprises more than 50 percent by weight based on total weight of the polymers of a polyurethane elastomer and at least a minor amount of a polymer selected from the group consisting of polyamides, polyvinyl acetate, polyvinylchloride, cellulose acetate, polyacrylonitrile, acrylonitrile-vinyl chloride copolymer and acrylonitrile-butadiene-styrene terpolymer.

3. The process of claim 1 wherein the solvent of the polymer solution is selected from the group consisting of acetone, tetrahydrofurane, acetonitrile, dimethyl sulfoxide, N ,N- dimethyl formamide, N,N-dimethyl acetoamide, tetramethyl urea and mixtures thereof.

4. The process of claim 1 wherein the nonsolvent is selected from the group consisting of water, methanol, ethanol, ethylene glycol and glycerin.

5. The process of claim 1 wherein water or an aqueous solution containing at least one member selected from the group consisting of solvents for the polyurethane elastomer and surface active agents is applied to the fibrous base in step l) in an amount of from 20 to 100 percent by weight based on the weight of said base.

6. The process of claim I wherein the polymer solution contains particles of short fibers.

7. The process of claim 1 wherein the polymer solution contains particles of leather powder.

8. The process of claim 1 wherein the polymer solution contains particles of magnesium carbonate.

9. The process of claim 1 wherein the fibrous material is cloth.

10. The process of claim 1 wherein the fibrous material is knitted fabric.

11. The process of claim 1 wherein the fibrous material is a nonwoven fabric.

12. The process according to claim 1 wherein the interacting solution of step 2 is characterized by its ability to increase the adhesive strength between the fibrous base and the coagulated porous polymer layer.

13 The process of claim 5 wherein the aqueous solution contains less than percent by weight of the solvent for the polyurethane elastomer selected from the group consisting of tetrahydrofuran, acetonitrile, N ,N-dimethyl formamide, N,N- diethyl formamide and N,N-dimethyl acetoamide.

14. The process of claim 5 wherein the aqueous solution contains less than 14 percent by weight of at least one surface active agent selected from the group consisting of anion surface active agents, cation surface agents, nonion surface active agents and amphoteric surface active agents.

15. The process of claim 5 wherein the aqueous solution contains less than 90 percent by weight of a solvent for the polyurethane elastomer selected from the group consisting of tetrahydrofuran, acetonitrile, N,N-dimethyl formamide, N,N- diethyl formamide and N,N-dimethyl acetoamide and less than 1 percent by weight of at least one surface active agent selected from the group consisting of anion surface active agents, cation surface active agents, nonion surface agents and amphoteric surface active agents. 

2. The process of claim 1 wherein the polymer solution comprises more than 50 percent by weight based on total weight of the polymers of a polyurethane elastomer and at least a minor amount of a polymer selEcted from the group consisting of polyamides, polyvinyl acetate, polyvinylchloride, cellulose acetate, polyacrylonitrile, acrylonitrile-vinyl chloride copolymer and acrylonitrile-butadiene-styrene terpolymer.
 3. The process of claim 1 wherein the solvent of the polymer solution is selected from the group consisting of acetone, tetrahydrofurane, acetonitrile, dimethyl sulfoxide, N,N-dimethyl formamide, N,N-dimethyl acetoamide, tetramethyl urea and mixtures thereof.
 4. The process of claim 1 wherein the nonsolvent is selected from the group consisting of water, methanol, ethanol, ethylene glycol and glycerin.
 5. The process of claim 1 wherein water or an aqueous solution containing at least one member selected from the group consisting of solvents for the polyurethane elastomer and surface active agents is applied to the fibrous base in step (1) in an amount of from 20 to 100 percent by weight based on the weight of said base.
 6. The process of claim 1 wherein the polymer solution contains particles of short fibers.
 7. The process of claim 1 wherein the polymer solution contains particles of leather powder.
 8. The process of claim 1 wherein the polymer solution contains particles of magnesium carbonate.
 9. The process of claim 1 wherein the fibrous material is cloth.
 10. The process of claim 1 wherein the fibrous material is knitted fabric.
 11. The process of claim 1 wherein the fibrous material is a nonwoven fabric.
 12. The process according to claim 1 wherein the interacting solution of step 2 is characterized by its ability to increase the adhesive strength between the fibrous base and the coagulated porous polymer layer. 13 The process of claim 5 wherein the aqueous solution contains less than 90 percent by weight of the solvent for the polyurethane elastomer selected from the group consisting of tetrahydrofuran, acetonitrile, N,N-dimethyl formamide, N,N-diethyl formamide and N,N-dimethyl acetoamide.
 14. The process of claim 5 wherein the aqueous solution contains less than 1 percent by weight of at least one surface active agent selected from the group consisting of anion surface active agents, cation surface agents, nonion surface active agents and amphoteric surface active agents.
 15. The process of claim 5 wherein the aqueous solution contains less than 90 percent by weight of a solvent for the polyurethane elastomer selected from the group consisting of tetrahydrofuran, acetonitrile, N,N-dimethyl formamide, N,N-diethyl formamide and N,N-dimethyl acetoamide and less than 1 percent by weight of at least one surface active agent selected from the group consisting of anion surface active agents, cation surface active agents, nonion surface agents and amphoteric surface active agents. 